The present invention relates to a brake unit operated by a fluid under pressure in order to apply braking force to the wheels of a railway car.
In particular, the invention relates to a type of brake unit in which a fluid pressure operated piston acts via an actuator device to displace a brake push rod that moves in a direction perpendicular to the motion of the piston to control a brake shoe that is engageable with a wheel of the railway car.
In known arrangement, the actuator device is a wedge-shaped member that is bifurcated to straddle the thrust rod and is attached to the piston to move with it. Each segment of the bifurcated cam member has a reaction surface that interacts with a reaction roller that is rotatably mounted on the housing and an inclined thrust surface that interacts with a thrust roller that is rotatably mounted on the brake push rod.